Glutaraldehyde-crosslinked poly(vinyl alcohol)/halloysite composite films as adsorbent for methylene blue in water

Poly(vinyl alcohol) (PVA) and halloysite nanotube (HNT) composite films were prepared by solution casting methodology for enhanced adsorption of methylene blue (MB) dye. The synthesis protocol utilized biodegradable glutaraldehyde as a crosslinker for maximum interlocking between the polymer and clay. The prepared PVA/HNT films were examined using FTIR, SEM, XRD, TGA, BET and PZC techniques. The adsorption parameters such as pH, contact time, HNT loading and adsorbent dose were suitably optimized. The study revealed 40 min contact time with 0.15 g adsorbent in 50 mL adsorbate solution can effectively bind MB with no prior pH adjustments. The monolayer adsorption capacity obtained for MB on PVA/HNT composite was 555 mg/g. Four adsorption isotherms and five kinetic models were studied to understand the adsorption process. The results showed that Langmuir isotherm (R2 ≥ 0.9829) and pseudo second order (R2 ≥ 0.9988) model fitted well with the experimental data. The negative Gibbs free energy values confirmed favourable adsorption, whilst positive enthalpy (55.54 kJ/mol) displayed endothermic nature for phenomena. Additionally, the recyclability studies showed practically no significant change in adsorption efficiency for at least 6 sorption-desorption cycles on the same PVA/HNT adsorbent. The results demonstrate excellent adsorption properties of PVA/HNT, further authenticating its relevance for treating wastewater samples containing MB.